Have you tried unauthorising the computer, through iTunes, then reauthorising it?
Edit - How big's the Sim city app? Did you download it on the iPhone? (just i have a recolleciton of another thread having issues with syncing a large app (myst i think )that they'd downloaded onto their iPhone, and then tried to sync with itunes.)
Maybe also try deleting Sim app if it's a large app, doing the unauthorise, reauthorise above, then downloading the app through itunes, and then sync through itunes again.